Piezoelectric Mechanism and a Compliant Film to Effectively Suppress Dendrite Growth

Abstract

We show a piezoelectric mechanism that effectively suppresses dendrite growth using a compliant piezoelectric film as a separator or coating. When an electrode surface starts to lose stability upon lithium deposition, any protrusion causes film stretching, generating a local piezoelectric overpotential that suppresses deposition on the protrusion. Lithium ions thus spontaneously deposit to a flat surface. By proposing a theory that couples electrochemistry and piezoelectricity, we quantify the suppression effect and growth morphology. We find that the dendrite-suppression capability is over 5 × 10 5 stronger than the limit of mechanical blocking by any separators or solid-state electrolytes. Surprisingly, the mechanism ensures deposition to form a flat surface even if the initial substrate surface has significant protrusions, suggesting its robustness and effectiveness against manufacturing defects. We show that the mechanism is so strong that even a weak piezoelectric material is highly effective, opening up a wide range of materials.

Multi‐Physical Field Simulation: A Powerful Tool for Accelerating Exploration of High‐Energy‐Density Rechargeable Lithium Batteries

“…Reproduced with permission. [ 54 ] Copyright 2020, American Chemical Society. e) Point deposition current density along the Li metal surface.…”

“…A dendrite suppression mechanism has been investigated by Lu et al [ 54 ] combining the electrochemistry and piezoelectricity, which effectively impedes the growth of Li dendrites and stabilizes the Li metal anode by coating the piezoelectric and compliant film on the Li metal. To further explore the mechanism of this compliant film, a numerical model based on the Fick's law and Butler‐Volmer equation has been built with the introduction of piezoelectric overpotential caused by strain (Figure 7c): $$$$\begin{equation}\dot{\varepsilon } = \frac{{\left( {R + {\upsilon }_ndt} \right)\delta \theta - R\delta \theta }}{{R\delta \theta dt}}\ = \frac{{{\upsilon }_n}}{R}\ = \ \kappa {\upsilon }_n\end{equation}$$$$…”

“…In addition to this, the surface electric field can be tuned by applying the dielectric materials. [53] A dendrite suppression mechanism has been investigated by Lu et al [54] combining the electrochemistry and piezoelectricity, which effectively impedes the growth of Li dendrites and stabilizes the Li metal anode by coating the piezoelectric and compliant film on the Li metal. To further explore the mechanism of this compliant film, a numerical model based on the Fick's law and Butler-Volmer equation has been built with the introduction of piezoelectric overpotential caused by strain (Figure 7c):…”

“…d) The electric field distribution with the morphology evolution started with a significant initial protrusion covered with a piezoelectric film. Reproduced with permission [54]. Copyright 2020, American Chemical Society.…”

A Single‐Layer Piezoelectric Composite Separator for Durable Operation of Li Metal Anode at High Rates

“…[17] Many functional separators with evenly distributed pore structures and regular pore sizes have been developed to achieve stable plating/stripping of Li metal. [18,19] In addition, a straininduced piezoelectric β-PVDF separator is studied to prohibit dendrite growth, but its electrochemical performance in LMBs needs further exploration, [20,21] and the shrinkage of the porous PVDF separator due to the heat produced during high-current cycle also requires profitable remedies. Moreover, modified separators with functional groups absorbing Li-ion at molecular level enable the formation of a uniform ion flux even at large current densities.…”